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ServletContext 对象代表整个web应用，可以和程序的容器(服务器)来通信

一、获取方法

（1）通过 request 对象获取：request.getServletContext();（2）通过 HttpServlet 获取：this.getServletContext(); -- 更常用

@WebServlet("/servletContextDemo1")public class ServletContextDemo1 extends HttpServlet {       protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {           /*            ServletContext对象获取：                1. 通过request对象获取			        request.getServletContext();                2. 通过HttpServlet获取                    this.getServletContext();         */                //1. 通过request对象获取        ServletContext context1 = request.getServletContext();        //2. 通过HttpServlet获取        ServletContext context2 = this.getServletContext();        System.out.println(context1);        System.out.println(context2);    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {           this.doPost(request,response);    }}

二、功能

1. 获取 MIME 类型：

* MIME类型:在互联网通信过程中定义的一种文件数据类型* 格式： 大类型/小类型	* 例如 text/html，image/jpeg* 获取：String getMimeType(String file)

@WebServlet("/servletContextDemo2")public class ServletContextDemo2 extends HttpServlet {       protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {                   //通过HttpServlet获取        ServletContext context = this.getServletContext();        //3. 定义文件名称        String filename = "a.jpg";//image/jpeg        //4.获取MIME类型        String mimeType = context.getMimeType(filename);        System.out.println(mimeType);    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {           this.doPost(request,response);    }}

2. 域对象：共享数据

（1）setAttribute(String name,Object value)（2）getAttribute(String name)（3）removeAttribute(String name)* ServletContext对象范围：所有用户所有请求的数据

和 共享数据一样，但是比 request 作用范围更广，所以需要谨慎使用

3. 获取文件的真实(服务器)路径

方法：String getRealPath(String path)  				 * String b = context.getRealPath("/b.txt");//web目录下资源访问		   * String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问		    * String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问

@WebServlet("/demo")public class ResponseServlet2 extends HttpServlet {       protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {           ServletContext context = this.getServletContext();        String path1 = context.getRealPath("/WEB-INF/classes/a.txt");        String path2 = context.getRealPath("/b.txt");        String path3 = context.getRealPath("/WEB-INF/c.txt");        System.out.println("a.txt --> " + path1);        System.out.println("b.txt --> " + path2);        System.out.println("c.txt --> " + path3);    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {           this.doPost(request, response);    }}